Screws of the type with which the present invention is concerned are commonly used to drill and tap holes in sub-structures such as steel wall studs or other sheet metal, for applications such as attaching insulation to a decking or roof. Fasteners of this type generally include a point at one end of the fastener for initiating a hole in the sub-structure. Moving up the shank, the fastener generally includes male threads to tap the hole in the sub-structure and terminates in a head having a recess into which a conventional driving tool can be inserted.
Examples of known fasteners include the screw disclosed in U.S. Pat. No. 2,015,159 "Rosenberg", hereby incorporated by reference. The Rosenberg screw has a piercing point which is designed to pierce or punch a hole in the substrate material prior to forming threads in the substrate. One disadvantage of a piercing point is that it will dull and will fail to pierce completely through when the substrate is a heavy gage metal. Thus it can be used only with thin or soft substrate material. Another disadvantage is that a piercing point provides no means for controlled extrusion of the substrate material. Other known fasteners include the screws shown in U.S. Pat. Nos. 3,093,028 "Mathie", 3,682,038 "Lejdegard", and 3,221,588 "Wieber", all of which are hereby incorporated by reference. These screws have a drilling point which overcomes some of the problems associated with a piercing point, but they also have cutting threads designed to cut the substrate material away in order to tap threads in the substrate, rather than extruding the hole and forming substrate threads. In most cases these fasteners require high axial end loading to accomplish point penetration and thread pick-up.